The present invention relates to systems for ultrasonic inspection of the interior of an object.
Acoustic sensing devices, such as ultrasonic inspection equipment, are used in inspecting the interiors of a variety of objects, including the human body, the area around a weld, and manufactured products such as wood-based panels. The performance of an ultrasonic inspection device is often limited by its ability to couple ultrasonic energy into the object to be inspected. When the ultrasonic waves travelling in air reach a solid surface, much of the energy is reflected away. This reflected energy is then not available to interact with the interior of the object, and it cannot contribute to a measurement of its internal properties. In some applications, placing the ultrasonic transmitter in hard physical contact with the object to be measured can solve the problem. In other applications, the coupling is improved by creating a liquid path between the transmitter and the object. However, use of these techniques is not always possible. It is often desirable to minimize or eliminate contact between the transducer and the object, leaving air-coupled transducers as the only possibility. Therefore, there is a need for an ultrasonic inspection system capable of increasing the energy coupled via air from a transmitter into a solid object and on to a receiver.
One method of increasing the energy coupled into the object and on to a receiver is to carefully control the positioning of the transducers relative to the object. The ideal positioning will depend on characteristics of the acoustic energy, notably the wavelength. The wavelength of an acoustic wave in air will vary with the physical properties of the air, including its temperature, humidity, and pressure. Therefore, there is a further need for an improved air-coupling system that is not affected by the properties of air. Finally, the application of the system may be to the processing of a moving object. Therefore, there is a further need for a method that does not require repeated measurements at the same location.
The disclosed embodiments of the present invention provide a means of increasing the effective coupling of ultrasonic energy from a transmitter to a solid object, and from the solid object to a receiver, using air as the coupling medium. The present invention further provides an air-coupled system that is not affected by changing properties of the air.
To achieve the foregoing, a method for increasing the coupling in an ultrasonic inspection system is disclosed that incorporates at least one pair of opposed transducers. One transducer in the pair acts as a transmitter, the other as a receiver. The vibrating face of the transmitter is positioned parallel to the surface of the object to be inspected. In this way, acoustic wave energy that is reflected from the object will travel back to the face of the transducer and be reflected once again to the object. The acoustic energy coupled into the object then travels through the object, interacting with its interior. It emerges from the far surface of the object, where the receive transducer is again positioned parallel to the surface of the object.
Because the acoustic energy exists as a wave, the energy reflected at a surface may either add to or subtract from the continuing energy emanating from the surface. When the distance between transducer and object equals a multiple of one-half of the wavelength of the acoustic signal, the reflected energy will add to the continuing energy. Under these circumstances, the space between the transducer face and the object will act as a reverberation chamber; the amount of acoustic wave energy will increase to a peak value. Therefore, the mounting apparatus for the transducers allows them to be initially positioned at a distance from the surface of the object of approximately one-half the wavelength. A processor is used to adjust the frequency of the transmitted signal so that the spacing will in fact be one-half the wavelength of the acoustic wave energy.
In accordance with the disclosed embodiments of the present invention, an acoustic sensing method is provided that includes generating an initial acoustic energy wave or set of acoustic energy waves at a nominal frequency and successive acoustic energy waves or sets of acoustic energy waves through an object. Each successive acoustic energy wave or set of successive acoustic energy waves is generated at a different frequency than the previous acoustic energy wave. The method further includes sensing the initial and successive acoustic energy waves from the object and determining the frequency of the sensed acoustic energy wave having the highest energy level, then changing the nominal frequency to the determined frequency.
In accordance with another aspect of the invention, the successive frequencies are changed both up and down by an incremental value, and then changed again both up and down by a second incremental value. Ideally, the second incremental value is a multiple of the first incremental value.
In accordance with another aspect of the disclosed embodiments of the present invention, an ultrasonic examination system for examining an object is provided. The system includes a microprocessor configured to generate frequency signals; a first transducer configured to receive the frequency signals and adapted to generate acoustic energy waves into the objects; a second transducer adapted to receive acoustic energy waves from the object and to generate corresponding energy value signals to the microprocessor, where the microprocessor is configured to adjust the frequency signals in response to the energy value signals to be at the frequency associated with the highest energy value signal.
In accordance with another aspect of the present invention, a method for acoustic sensing of an object in a computer-controlled system is provided. The method includes performing a plurality of acoustic energy measurements of the object at a nominal frequency and then at different successive frequencies; determining the measured acoustic frequency having the highest acoustic energy, and changing the nominal frequency to the determined frequency. Ideally, the method includes repeatedly performing the plurality of acoustic measurements and determinations.